1. Field of the Invention
The present invention relates to a semiconductor storage device having capacitive elements and a method of manufacturing the semiconductor storage device, and in particular relates to a method of forming a dielectric film using a metal organic chemical vapor deposition method.
2. Description of a Related Art
In recent years, research and development has been carried out with vigor into ferroelectric memories that utilize the polarization characteristics of a ferroelectric, DRAMs that use a high-dielectric-constant material, and so on.
As methods of forming a film of a ferroelectric or a high-dielectric-constant material, conventionally a sol-gel method, a sputtering method, a CVD method and so on have been used. Of these methods, the CVD method is superior in terms of the uniformity of film formation over a large-diameter wafer and the ability to cover over steps on the surface, and hence is promising as an ULSI mass production technique.
As methods of forming a film of a ferroelectric or a high-dielectric-constant material using such a CVD method, in particular a metal organic chemical vapor deposition (MOCVD) method, the following methods have been disclosed.
Japanese Unexamined Patent Application Publication No. 2000-58525 discloses a vapor phase deposition method for a metal oxide dielectric film (in particular a PZT film) having a perovskite-type crystal structure represented by general formula ABO3, the deposition method having a step of forming an initial nucleus or initial layer having a perovskite-type crystal structure on a conductive material under first film formation conditions, and a step of further forming a film having a perovskite-type crystal structure on the initial nucleus or initial layer under second film formation conditions. Furthermore, it is stated that the raw material supply amounts for the constituent elements are changed between the first film formation conditions and the second film formation conditions. Moreover, it is disclosed that according to this method, the film formation can be carried out at a low temperature (450° C. or less) so as not to cause degradation of plugs, wiring and transistors in a lower layer, and moreover a metal oxide dielectric film having excellent orientation and crystallinity can be formed.
Japanese Unexamined Patent Application Publication No. 2002-334875 discloses a vapor phase deposition method for a metal oxide dielectric film (in particular a PZT film) having a perovskite-type crystal structure represented by general formula ABO3, the deposition method having a step of forming an initial nucleus or initial amorphous layer having a perovskite-type crystal structure on a conductive material under first film formation conditions, and a step of further forming a film having a perovskite-type crystal structure on the initial nucleus or initial amorphous layer under second film formation conditions, and characterized in that here the first film formation conditions satisfy at least one of the substrate temperature being lower than for the second film formation conditions and the raw material gas pressure being higher than for the second film formation conditions. Furthermore, it is stated that according to this method, a dielectric film is formed for which the leakage current is low and moreover the transparency is excellent and hence mask alignment can be carried out well, and furthermore if this dielectric film is used in a capacitive element then a semiconductor device having little variation in bit line voltage difference can be manufactured.
However, with the method of forming a dielectric film using the MOCVD method having two steps as in the conventional art described above, there have been calls for further improvements with regard to the capacitance characteristics of the element formed.